The object of the present invention is a process for producing guarseed flour which, when it is dissolved in water, produces a transparent solution of high viscosity, where the process produces good yields of the pure flour despite extensive cleaning. Transparent, high-viscosity solutions of pure guarseed flour are of great importance primarily in the food industry.
Guarseed flour is used as a thickening agent in the textile and explosives sectors, as a binding agent in the paper industry, as a flocculant in ore extraction and as an auxiliary material in the extraction of natural gas and oil, in the pharmaceutical and cosmetic fields, and as a thickener, emulsifier and (co-)stabilizer in the areas of foods and food technology.
In pharmaceutics guarseed flour is used for example for spray embedding of vitamins, in order to increase their shelf stability. In addition, the use of guarseed flour in sprays guarantees nearly monomolecular distribution of the active ingredients and consequently improved, uniform resorption, which is desirable in the case of asthma medications and various allergy remedies. Because of the extremely low protein content of the pure guarseed flour there is no danger of the development of an allergic reaction to a medication which contains this substance. Additional applications in this field are the formulation of delayed-action tablets and as a means of lowering the cholesterol level. In the field of medicine guarseed flour is also used as an emulsifier and stabilizer in contrast agents.
Among other applications, guarseed flour has also proven to be an ideal dietetic substance, since its building blocks, the so-called galactomannans, are not attacked by human stomach and intestinal enzymes. This is to be expected, since in the human digestive system up to the large intestine there are neither xcex2-mannanases nor xcex1-glacto-sidases present, which would be necessary to break down these building blocks. Since the building blocks of guarseed flour do not enter into the human metabolism, there is no reason to regard guarseed flour as a carrier or supplier of calories. Since guarseed flour is constituted of completely neutral polysaccharides, or more precisely of galactomannans, which have neither uronic acid nor other ionogenic groups, they represent a completely harmless material in physiological terms.
An additional advantage in terms of its use as an ingredient in foods is its complete neutrality of taste. It is used in reduced-calorie or reduced-fat foods or drinks which are often perceived as xe2x80x9cthinxe2x80x9d by the consumer. Adding guarseed flour to these products lends them a xe2x80x9ccreamierxe2x80x9d consistency. In the production of fruit juices guarseed flour is used in order to re-suspend the fruit pulp uniformly, in puddings and cremes it functions as a thickener, in ice creams, milkshakes, mousses and similar products it works as a stabilizer. With traditional guarseed flour preparations, only mild molecular interaction with the biopolymer xanthane was found. While mixing these two colloids did produce a synergistic increase in viscosity, a specific formation of gel as in the case of carubin, carob seed flour and xanthane, did not occur. If a 1:1 mixture of the guarseed flour in accordance with the invention and xanthane is heated together and allowed to cool at 4xc2x0 C. (refrigerator temperature), a gel forms. An advantage of this combination of guarseed flour and xanthane lies in the fact that the gel from these two components melts at body temperature, so that it is superbly suited for the production of gelatin-like foods, as a vehicle for the delivery of medications in pill form, and the like. Furthermore, guarseed flour and xanthane are used in combination as co-stabilizers in the production of salad dressings, since this combination, in contrast to guarseed flour used alone, is resistant to acids.
Guarseed flour is obtained from the endosperm of the guar bean (cyamopsis tetragonobolus). Guarseed flour consists in large measure of galactomannans, i.e. of polysaccharides whose fundamental chain is linked in the 1xe2x86x924 direction by xcex2-glycoside bonds and is made up of mannose which is joined to galactose via primary OH groups. The ratio of unsubstituted mannose to mannose substituted with galactose is about 2:1, with the substituted units not alternating strictly but arranged in the polygalactommannan molecules in groups of two or three. The guar-galactomannans form highly viscous solutions in water even in slight concentrations. Acueous solutions of 1 percent by weight of common commercial guarseed flour produce viscosities of around 3000 to 6000 mPaxc2x7s.
Guar-galactomannans are divided into cold water soluble, hot water soluble and insoluble galactomannans on the basis of chemical and physiochemical differences.
To obtain and purify the guarseed flour the guarseed is treated mechanically; this produces approximately 35 parts unrefined guar endosperm halves and approximately 60 parts guar germ flour. The guar germ flour consists primarily of the germ of the seed, the scraped off bean skin, and small pieces of the endosperm. The endosperm completely encloses the germ and is in turn surrounded by the seed skin. A protein-rich, aleuron-like cell layer encloses the endosperm, whose cells are closely interlocked with the endosperm. This protein-rich layer adjoins the seed skin.
The unrefined endosperm halves can be further cleaned mechanically and produce splits of varying quality in terms of their protein content, their components which cannot by hydrolyzed by acid (A.I.R.) and the amount of skin present. The term xe2x80x9csplit,xe2x80x9d which is usual among the specialists, is synonymous with the term xe2x80x9cendosperm halves.xe2x80x9d
Although guarseed flour is already in wide use as a thickening agent, there is a desire to improve its purity and, related thereto, its physical and physiological properties. For its use in foods, in particular, the purity of the guarseed flour is of great importance. Also desirable is more complete utilization of the main components of the endosperm, so that the latter can be used to a greater degree in the corresponding branches of industry in place of cellulose derivatives or other polysaccharides which are clearly soluble in water, or synthetic polymers which are clearly soluble in water.
If the products consisting of pure guarseed flour which are currently available on the market, when processed into flour, are dissolved in water at 25xc2x0 C. or at 86 to 89xc2x0 C. for 10 minutes, they produce cloudy solutions. If the insoluble material in these solutions is centrifuged out at high centrifugal forces ( greater than 35,000xc3x97g), it turns out that 23-35% of the guarseed flour comprises material which is centrifuged out. Microscopic investigations have shown that the centrifuged precipitate is made up primarily of skin fragments, protein materials, insoluble peripheral cells, intact unopened cells of the inner endosperm and other impurities of the seeds or splits. Chemical derivatization of the guarseed flour (etherification, hydroxypropylation, cationization, etc.) makes it possible to produce products with significantly improved dissolving behavior in water, and along with that, greater transparency of the solutions.
One of the processes used heretofore for obtaining pure guarseed flour uses chlorinated solvents, such as trichlorethylene (see EP 0 130 946, Meyhall Chemical AG). The solution was fractionated by simply being left to stand or by centrifuging, which led to the formation of a protein-rich fraction (floating fraction) and the separation of a protein-poor fraction (precipitating fraction).
It has been possible to show that the highest floating fraction of endosperm processed into flour, such as guar CSA 200/50, can contain up to 25% proteins, and the precipitating fraction, which makes up 75% of the pure flour, contains about 1.5 to 1.6% protein. The precipitating fraction is used for example to produce cationic derivatives, which can be dissolved to produce clear aqueous solutions. A disadvantage of this process is that finely-ground skin fragments are also found in the precipitating fraction. An additional disadvantage is the use of halogenated solvents, since a specific weight of 1.47 to 1.48 kg/l is required. Proteins have a density of 1.3 kg/l and the galactomannans a density of 1.5 to 1.55 kg/l depending upon their moisture content. The guarseed flour produced by the process described here is suited primarily for technical applications. In food preparation this guarseed flour is probably not usable, since remnants of the halogenated solvent which was used remain in the end product; 10 ppb are found in fractions extracted with ethanol. Halogenated solvents are toxic and caustic to varying degrees, and frequently possess allergizing properties. This process should be avoided for environmental reasons as well.
An additional process for producing pure guarseed flour was proposed as early as 1969. It comprised an alkali treatment of pre-swollen splits at elevated temperatures, in which 100 parts of alkali were absorbed by 100 parts of SPS. The large quantity of alkali, i.e. NaOH, had to be washed out. This was carried out with cold water at a proportion of 1:80 (SPS:H2O) and in a water extraction step with isopropanol (IPA), in which at the same time the residual NaOH in the purified splits was neutralized with acetic acid.
After grinding, a pure guarseed flour of high quality was obtained in a yield rate of 60-70%, based on the raw material SPS (simply purified splits). In 1969 this process was improved by Stein, Hall and Co., Long Island City, N.Y. The present washing process with water is based on that process. The purpose of this process for purifying guar derivatives is to remove skin fragments and peripheral cell layers, and also to remove byproducts of the various etherification reactions (hydroxypropylation, carboxymethylation and cationization and/or combinations of these).
Despite the intensive purification processes described above, it has not yet been possible to obtain in an economical way pure, non-derivatized guarseed flour which produces a clear aqueous solution with high viscosity whale at the same time delivering good yields.
The disadvantages of the processes used to date for purifying and obtaining pure guarseed flour are:
1. large losses of valuable portions of the endosperm during the mechanical cleaning, and resultant small yields of pure guarseed flour in proportion to the source material;
2. skin fragments which continue to be found on the splits of varying quality, and which interfere with the functioning of the modified end products to a large extent;
3. peripheral, protein-rich cells of the aleuron layer which hardly swell in water and which likewise have a negative influence on the functioning of the end product;
4. presence of other impurities from the guarseeds, such as woody particles, which should not be present.
It was desired, therefore, to develop a process for producing pure guarseed flour which would eliminate the aforementioned disadvantages and deliver good yields of pure guarseed flour which, after dispersion in water, would produce a clear, highly viscous solution, to be used primarily for example in the food industry, the pharmaceutical and paint industries, and in the extraction of oil.
The objective of the present invention is to fulfill the aforementioned requirements, i.e. to obtain good yields of pure guarseed flour through a new production process, especially guarseed flour suitable for the food industry, which produces clear aqueous solutions of high viscosity.
The process according to the invention for producing pure guarseed flour is defined in patent claim 1, and comprises the following stages:
(a) treatment of guar splits with acid;
(b) one-time or repeated washing of the acid-treated splits with water and/or neutralization with an aqueous alkaline solution;
(c) treatment of the splits with an aqueous alkaline solution;
(d) washing the splits with water;
(e) extraction of the water from the splits with an acueous alcohol solution.
A first prerequisite for obtaining pure guarseed flour is to improve the starting material, the so-called splits. The splits, covered with skins, should constitute up to 42.5% of the seed by weight. The overlapping skin-endosperm portions, which amount to 13.5 percent of the seed by weight, are essentially insoluble in water. The embryo of the seed makes up the remaining 44%. These quantity indications show that the theoretical yield of splits usable for the invention, without skin and without overlapping parts, is 32%.
The pure guarseed flour according to the invention can be produced most advantageously from splits which have a protein content of 4.2% and an A.I.R. proportion of 1.8%.
Pure guarseed flour, whose source material according to the invention preferably consists of splits of the highest purity available at the time, can be produced after acid treatment using 70% to 96%, preferably 96%, sulfuric acid (8% to 12% based on the weight of the split) at room temperature or elevated temperatures. If the concentration of the sulfuric acid is lower than 70% by weight, then smaller yields of pure guar products are produced, and in addition with lower viscosities.
The order of the various steps of treatment after the acid treatment can be varied, which causes the resulting guarseed flour to acquire differing properties in terms of its viscosity, translucency, protein and A.I.R. content. For example, the order of the handling steps can be chosen from the following technical sequences, to name just a few possibilities:
1. washingxe2x80x94alkaline treatmentxe2x80x94washingxe2x80x94water extraction and neutralization as needed, preferably with an organic acidxe2x80x94drying and/or grinding
2. neutralization of the acid-treated splitsxe2x80x94washingxe2x80x94alkaline treatmentxe2x80x94washingxe2x80x94water extraction and neutralization as needed, preferably with an organic acidxe2x80x94drying and/or grinding
Dehydration with isopropyl alcohol or some other alcohol such as methanol, ethanol, N-propyl alcohol, N-butyl alcohol or equivalent is an absolute xe2x80x9cmust,xe2x80x9d if good products are to be produced. Treatment with IPA improves the clarity of the aqueous guarseed flour solutions. If appropriate, at the same time as the IPA treatment a neutralization with 99% acetic acid or some other so-called food acid such as citric acid, tartaric acid, formic acid or equivalent can be performed.
The level of moisture during the grinding significantly influences the properties of the mealy end product. The higher the moisture content in a technically practicable dimension, the larger is the quantity of the soluble polysaccharides, i.e. the higher is the yield of active galactomannans. This can be explained by the enlargement of the cell volume due to the high degree of moistening. During the grinding the swollen cells are forced through a defined opening or crack, which can cause the cell membrane to tear, assuming that the swollen particles are significantly larger than the openings (the elasticity of the cells also plays an important role). When solutions in water are produced the galactomannans are released from the cells which have thus been destroyed, which is not the case with cells which have not been destroyed. In these cases the galactomannans remain within the intact cells and do not contribute effectively to the viscosity of the solution.
A moisture content of approximately 72% to 75% when grinding is acceptable for practical and technical reasons. Moisture levels lower than 72% when grinding lower the quality of the guarseed flour. A higher content does not offer any advantages.
An advantage of the present invention consists in the possibility of producing products for solutions with viscosities for example as low as 45 mPaxc2x7s, and those with up to 9000 to 10000 mPaxc2x7s at 1% concentration in water at 25xc2x0 C.
An additional advantage of the invention consists in producing pure guar products whose protein content is as low as 0.2 to 0.5.
The yield of pure guarseed flour varies between 70% and 80%.
Adding borax during the alkaline treatment or during a washing step makes the purifying process significantly easier. Excessive moistening or swelling can be prevented by 0.05% borax, based on the weight of the source split. The end product is unsuitable for use in foods after addition of borax, however, since traces of borax (approximately 20 ppm) remain in the end product.
Derivatization of the galactomannans in the guarseed flour is a significant factor in the latter""s solubility in cold water. Through derivatization (e.g. carboxymethylation, hvdroxypropylation and the like) one or more non-ionic, anionic or cationic groups are added, causing the galactomannans which are soluble in hot water to become cold-water soluble. The derivatization usually takes place immediately following the cleaning. As in the case of the addition of borax, as mentioned above, the use of derivatized guarseed flour is not allowed in the food industry. Derivatized guarseed flour, especially guarseed flour which is derivatized by cation activation, does however find use in such cosmetic products for instance as hair conditioner, body lotions and similar products.
The material resulting from the present invention is especially advantageous, in that when dissolved in water it yields solutions of great clarity. A 1% solution (0.9% dry substance) of the pure guarseed flour produced with this process shows a viscosity of 9000 to 10000 mPaxc2x7s at 25xc2x0 C., when such solutions are produced in a household mixer using hot water at 90 to 100xc2x0 C. The very high-viscosity products have a protein and an A.I.R. content of only 0.2 to 0.6%. Through selection of the necessary processing steps (acid treatment, washing with water, treatment with IPA), an aqueous solution with a transparency of up to 94% can be achieved. A 0.5% solution of the pure guarseed flour with extremely high viscosity at a wavelength of 500 nm with a 1 cm cuvette at 25xc2x0 C. shows a clarity of 74 to 81%, whereas untreated split solutions which have been produced at the same concentration and temperature show a translucency of 46 to 48%. The comparable clarity of solutions of the precipitating fraction mentioned earlier, obtained by fractioning ground guar products in halogenated or fluorinated hydrocarbon, is around 56%. The viscosity was determined in a Brookfield RVT viscometer, the transparency of the solutions in a photospectrometer.